Solidification Structure and Macrosegregation of Billet Continuous Casting Process with Dual Electromagnetic Stirrings i
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id steel solidification, the grains nucleate from the liquid phase and the solute element is rejected from the solid dendrites. With the effect of fluid flow, the solute element is carried away and transports in a long distance, which leads to the formation of macrosegregation.[1] It should be noted that the macrosegregation in the strand cannot be removed by the subsequent heat treatment or rolling process, and it affects the product properties.[2] The electromagnetic stirring (EMS) technology, which makes fluid move around and controls liquid steel solidification, has already been one of the effective methods to improve strand quality during the past decades. To have an in-depth understanding of EMS effect on fluid flow, solute transport, and solidification structure, numerous plant trails or simulations have been carried out. Liu et al.[3] used a simulation method to calculate 3D electromagnetic field and fluid flow in a round-bloom D. JIANG, Ph.D. Candidate, and M. ZHU, Professor, are with the School of Metallurgy, Northeastern University, Shenyang 110819, P.R. China. Contact e-mail: [email protected]. Manuscript submitted December 2, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
with M-EMS. The results showed that the distribution of electromagnetic force and magnetic flux density was not uniform and the electromagnetic stirring had an important influence on the slag distribution. With the mold wall temperature assumed as the liquidus temperature, Yu and Zhu[4] studied the distribution of flow field, temperature field, and inclusion trajectory in a round billet with M-EMS and some plant trials were also carried out. The strand central porosity and surface defects were improved obviously with the optimum stirring parameters of M-EMS. As Darcy’s law was introduced to account for the effect of solidification on fluid flow, Song et al.[5] applied a 3D unsteady mathematical model to analyze the molten steel flow and billet solidification with EMS. The results showed that the temperature in the liquid core decreased quickly and the molten steel flow pattern was changed, which were a benefit for the improvement of central shrinkage cavity and macrosegregation. Sun and Zhang[6] presented a 3D and 2D hybrid method to simulate fluid flow and solute transport during the bloom continuous casting process. The formation of positive and negative segregation was ascribed to the floatation of solute-rich molten steel and the washing effect of the electromagnetic stirring flow. Mizukami[7] carried out laboratory experiments and found V-segregation could be eliminated by the F-EMS,
while the sufficient amount of fine equiaxed grains was a precondition. Ayata et al.[8] undertook many plant trials and laboratory experiments to investigate the EMS effect on the solidification process. The center segregation was reduced by the combination of M-EMS and F-EMS, and there was an optimum stirring condition for F-EMS. Oh[9] conducted a series of plant tests to investigate the effect of EMS modes on macrosegregation improvement. It was found that the solidification end w
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